DEVELOPMENT OF TEETH

1. DEVELOPMENT OF TOOTH

5. OVERVIEW OF TOOTH DEVELOPMENT
• Teeth develop as a result of the interaction between
oral epithelium and underlying mesenchyme.
• 20 primary tooth germs develop initially with 32
additional tooth germs differentiate to form the
permanent dentition.
• Each tooth germ develops as an anatomically distinct
unit .
• The fundamental developmental process is similar
for all teeth.

6. • Each tooth develops through
1. Bud ,
2. Cap and
3. Bell stages
• These are based on morphology of tooth germ

7. • Tooth development is also classified based on
physiological stages which are
• 1. Initiation,
• 2. Proliferation,
• 3. Histodifferentiation,
• 4. morphodifferentiation
• 5. eruption.

8. • The formative cells of tooth germ differentiate
to form dentine and enamel.
• Tooth erupts and is covered by periodontal
ligament and bone.
• Root formation proceeds till the tooth is in
functional position.

9. Primary Epithelial Band
• The primitive mouth or stomatodeum is lined by 2-3 cell thick
epithelium which covers the underlying connective tissue.
• At 37th day of development a continuous band of epithelium
forms which is horse shoe shape and corresponds to the
future dental arches and lower jaw.
• This is not due to increased proliferative activity but change in
orientation of the cleavage plane of dividing cells
• This leads to form a band of thickened epithelium which
grows into the underlying ectomesenchyme.

12. • This undergrowth has two subdivisions
• 1. The vestibular lamina
• 2. The dental lamina

14. • Section through the
lower jaw of an embryo.
The tongue (upper
right), Meckel's
cartilage (lower right),
bone spicules (lower
center), oral mucosa
and the dental lamina
(center) are visible. The
section passes through
a tooth bud, which is a
further extension of the
dental lamina into the
mesenchyme around
this very early tooth germ.

15. • Higher magnification of the oral epithelium and dental lamina,
which extends into the underlying mesenchyme. Bone spicules
can be seen near the bottom.

16. • Oral mucosa (above), dental lamina (right), and vestibular lamina (left)
are present. The vestibular lamina will eventually split, forming the
primitive vestibule of the mouth (the space between lips or cheeks and
the tooth-bearing areas of the jaws).

17. Vestibular lamina
• If a section of developing head region of an
embryo at 6 weeks is examined, no vestibule
or sulcus can be seen between cheek and
tooth bearing area.
• The vestibule is as a result of vestibular lamina
into ectomesenchyme.
• The cells enlarge and degenerate to form the
sulcus which becomes the vestibule.

18. Dental Lamina
• Continious and localised proliferation leads to
formation of series of epithelial ingrowths into
the ectomesenchyme at sites corresponding
to positions of the future deciduous teeth.
• From this point the tooth development
proceeds in three stages which indicates the
morphology and doesn't describe the
significant functional changes.

19. Initiation of the tooth
• Odontogenesis is first initiated by factors
resident in the first arch epithelium
influencing the ectomesenchyme but with
time this potential is assumed by
ectomesenchyme.

20. Bud stage
• It is formed by the first epithelial incursion into the
ectomesenchyme.
• Continued and localized tissue proliferation leads to epithelial
outgrowth into ectomesenchyme.
• No change in size or shape or function.
• Underlying ectomesenchymal cells are closely packed around
the epithelial bud.
• Epithelial outgrowth is called enamel organ.
• Enamel organ has a shape to a bud.

21. •
Oral ectoderm
Dental lamina
Central Polyhedral cells
Ectomesenchymal cells
Peripheral cuboidal cells
BUD STAGE

23. Cap stage
• As epithelial cells continue to proliferate the cellular density
increases around the epithelial bud.
• The condensation of ectomesenchyme does not produce ground
substance and cells are not seperated from each others.
• The epithelial ingrowth which resembles a cap sitting on a ball of
condensed ectomesenchyme is called Dental organ or Enamel
Organ which gives rise to Enamel.
• The ball of ectomesenchymal cells is called the dental papilla which
gives rise to dentin and pulp.
• The encapsulating structure of enamel organ and dental papilla is
called Dental follicle which gives rise to cementum, Periodontal
ligament and supporting structure – Alveolar bone.

24. Cap stage
Oral ectoderm
Outer enamel epith
Stellate reticulum
Inner enamel epith
Dental sac
Dental papilla
Dental lamina

25. Cap stage
Oral ectoderm
Oral ectoderm
Outer enamel epithelium
Stellate reticulum
Inner enamel epithelium
Dental Papilla
Dental Sac

26. An early cap-stage tooth bud (left) and the adjacent vestibular lamina. The
mesenchyme adjacent to the tooth bud is beginning to condense.
Spicules of bone are present at the bottom

27. • Higher magnification of an early cap stage tooth bud. Mesenchymal cells that
will form the dental papilla are beginning to condense, and the mesenchyme
that forms the dental sac or follicle, surrounding the tooth bud, is beginning to
organize

28. Cap stage tooth bud. The tall columnar cells adjacent to the mesenchymal cells
forming the dental papilla will become the inner dental epithelium. The region
of widely-separated epithelial cells between the inner and outer dental
epithelial layers is the stellate reticulum. The forming dental sac is also visible.

29. TRASIENT STRUCTURES DURING TOOTH DEVELOPMENT
• Enamel knot, Enamel cord , Enamel Niche
1. Enamel Knot :- Localised thickening in the internal dental
epithelium at the centre of tooth germ.

30. 2. Enamel cord :-
The knot is continuous which is strand of cells running from
the knot to the external enamel epithelium.
The function of these two structures is not known but
possibly determine the crown pattern.

31. 3. Enamel Niche :-
• This structure is created by the plane of section cutting
through a curved dental lamina so that the mesenchyme
appears to be surrounded by dental epithelium. An artefact. It
gives an impression that the enamel organ is attached at two
sites.

32. Bell Stage

33. • Continuous growth leads to bell stage , so called
because the enamel organ has an invaginated
undersurface which resemble a bell.
• Epithelial cells transform into morphologically and
functionally distinct components
Four types of cell layers are seen,
• 1. Inner enamel epithelium
• 2. Outer enamel epithelium
• 3. Stratum intermedium
• 4. Stellate reticulum.
Early Bell stage
(Histodifferentiation and morphodifferentiaton)

34. • The cells in the centre of dental organ continue to
secrete glycosaminoglycans into extracellular
component which forces the cells apart.
• The cells retain their connections by desmosomes and
appear star shaped. So they are called Stellate
Reticulum.
• At the periphery of dental organ the cells assume a
cuboidal shape to form the outer or external enamel
epithelium.

35. • The cells bordering and adjacent to dental papilla assume a
short columnar shape with high glycogen content called the
inner enamel epithelium.
• Between inner enamel epithelium and stellate reticulum
some epithelial cells differentiate into a layer called stratum
intermedium. These cells are highly rich in enzyme alkaline
phosphate .
• Both the IEE and stratum intermedium are considered as a
single layer.
• The outer enamel epithelium meets inner enamel epithelium
at a zone known as Cervical Loop or Zone of reflexion.

36. •
BELL STAGE
Dental sac
Outer enamel epithelium
Stellate reticulum
Strarum intermedium
ameloblasts
Dental papilla
Cervical loop
Odontoblasts

37. A bell stage tooth germ. The
definitive shape of the dentino-
enamel junction (DEJ) is now
established by the dental papilla
and the inner dental epithelium.
The stellate reticulum and the
outer dental epithelium, but not
the stratum intermedium, are
visible at this low magnification.

38. • A bell stage tooth
germ. The stellate
reticulum, inner
and outer dental
epithelium, dental
papilla and dental
sac can be
identified. The oral
mucosa (above)
and developing
bone (below) are
also visible.

39. • Drawings of
the cap and
bell stages of
tooth
development
(left) and the
appearance of
these stages
in sections
(right).

41. THE FINE STRUCTURE OF TOOTH GERM IN
EARLY BELL STAGE
• The dental organ is supported
by a basal lamina.
• The external enamel
epithelium is cuboidal with
high nuclear cytoplasmic ratio.
• Their cytoplasm contains few
ribosomes, endoplasmic
reticulum, mitochondria,
tonofilaments.
• Adjacent cells are joined by
junctional complexes.

42. • The star shaped stellate
reticulum cells are
attached to each other,
to cells of OEE and
stratum intermedium by
desmosomes with fewer
cell organelles.
• The cells of stratum
intermedium are
connected to stellate
reticulum and IEE by
desmosomes and have
usual cell organelles.

43. • The cells of inner enamel
epithelium have a centally
placed nucleus with ribosomes,
RER mitochondria , high
glycogen content.
• The dental papilla is seperated
from enamel organ by a
basement membrane and an
acellular zone.
• These are undifferentiated
mesenchymal cells with usual
cell organelles and few collagen
fibres in between them.
• The dental follicle has more
collagen fibrils and generally
oriented in a radical pattern.

44. Crown pattern determination
Two important events takes place during bell stage
• 1. The dental lamina breaks up separating the
developing tooth bud from oral epithelium
• 2. The IEE folds which helps in recognizing the future
pattern of crown.
The IEE lies between two opposing pressures one from
stellate reticulum and other from growing dental
papilla which is contained by dental follicle. The crown
pattern is determined by differential rates of IEE.

45. • Cessation of mitotic activity within IEE leads to
differentiation and assume their eventual function of
producing enamel.
• So the point at which IEE cells differentiate represent
the future cusp position. Eventually a zone of
maturation sweeps down the cusp slopes.
• The occurrence of second zone of maturation leads
to formation of second cusp and soon until the
cuspal pattern of tooth is determined.

46. • How are the different shapes of teeth
determined ??
• Two hypothetical models have been proposed
• 1. Field Model
• 2. Clone Model

47. FIELD MODEL
• This proposes that the factors responsible for tooth
shape reside within ectomesenchyme in distinct but
graded fields for each tooth family.

49. CLONE MODEL
• The clone model proposes that each tooth class is derived
from a clone of ectomesenchymal cells programmed by
epithelium to produce teeth of a given pattern.
• The enamel knot also plays an important role with precise
expression of growth and transcription factors associated with
sites of future cusp formation.

50. •
Advanced Bell stage
Stellate reticulum
Enamel
Dentin
Odontoblasts
Outer enamel epithelium

51. Advanced bell stage
• Formation of dental hard tissues.
• Nutrition supply to ameloblast is cut off
from dental papilla.
• Stellate reticulum collapses.
• Enamel deposits at cusp tips.

52. Hard tissue formation or crown
stage
• The late bell stage is characterised by formation of two
principal hard tissues of the tooth i.e. the dentin and enamel
• At the future of cusp tips , the mitotic activity ceases , the
cells of IEE elongate to become tall columnar cells with
nucleus towards stratum intermedium.
• These changes in IEE leads to changes in the dental papilla.
The undifferentiated mesenchymal cells differentiate into tall
columnar cells called the odontoblasts - the dentin forming
cells. This increase in cell size eliminate the acellular zone.

53. • The odontoblast begin to secrete organic
matrix of dentin, collagen which ultimately
mineralizes .
• The odontoblasts move towards the dental
papilla leaving behind a cytoplasmic extension
around which dentin is formed.

54. • After the first dentin is formed , the cells of IEE
differentiate further into ameloblasts and secrete an
organic matrix against the newly formed dentinal
surface which is immediately partially mineralized to
become the enamel of crown.
• The ameloblasts move away from dentin.
• Odontoblast differentiate under organising influence
of cells of IEE and likewise enamel formation cannot
begin until dentin is formed. An example of
RECIPROCAL INDUCTION.

55. • Before the formation of dentin, the cells of IEE receive
nutrition from dental papilla and periphery of OEE.
• Once dentin is formed the nutrition from dental papilla is
reduced and so the stellate reticulum collapse so that the
ameloblasts are approximated closer to OEE and blood
vessels.
• The high glycogen content in cells of IEE is used to meet the
metabolic requirement until the stellate reticulum collapses.

56. •
Advanced bell stage

57. • Late bell or early
crown stage tooth
germ; matrix
apposition has begun
at the incisal tip.
• Outer dental
epithelium, stellate
reticulum, inner dental
epithelium, enamel,
dentin, predentin,
odontoblasts, dental
papilla and dental sac
can be identified.
• The tongue (upper
right) and lip with
developing minor
salivary glands (upper
left) are also visible

58. • Cusp tip of a tooth germ at a
similar stage of development.
Enamel and dentin formation
are underway. The dental
papilla with its odontoblasts
is below. External to the
odontoblasts are the
predentin (nearly colorless),
mineralized dentin (purple),
enamel (dark purple),
ameloblasts (tall columnar
cells), stratum intermedium
(flattened cells) and stellate
reticulum.

59. • An area nearer the cusp tip than the previous
micrograph. Pre-odontoblasts, inner dental
epithelium, stratum intermedium and stellate
reticulum can be identified

60. • Closer to the cusp tip, odontoblasts and the
very earliest predentin are now present.

61. • Even closer to the cusp tip, both predentin and dentin are present.
The cells of the inner dental epithelium, which are now becoming
preameloblasts, are increasing in height and their nuclei are
migrating to the proximal ends of the cells

62. • At the cusp tip, a
thin layer of
enamel (dark
purple) lies just
external to the
dentin. A layer of
tall ameloblasts
with proximally-
located nuclei,
flattened stratum
intermedium cells,
and the stellate
reticulum can be
identified.

63. • Membrana performativa is the basement
membrane, which separates the enamel
organ and dental papilla before dentin
develops.

64. ROOT FORMATION
• Root is made up of dentin.
• For cells of dental papilla to differentiate into odontoblasts.
Inner enamel epithelial is required.
• The inner enamel epithelium and outer enamel epithelial
proliferate to form a double layer of cells known as Hertwigs
Epithelial Roots Sheath (HERS).
• The HERS grows in between dental papilla and dental follicle
till it encloses the basal portion of papilla.
• The inner epithelial cells progressively enclose more of
expanding dental papilla and initiate the differentiation of
odontoblasts from cells at the periphery of the dental papilla.
In this way a single rooted tooth is formed.

66. • Multirooted teeth are formed in essentially
the same way.
• Two tongues of epithelium growing towards
each other form a collar which converts a
single in to two apical foramen
• three tongues forms a multirooted teeth.
• If the root continues to grow the root sheath
is stretched and disintegrates to form cluster
of epithelial cells, known as epithelial cell
rests of malassez.

68. FORMATION OF SUPPORTING STRUCTURES
• As the root sheath fragments, the
ectomesenchymal cells become opposed to
the newly formed dentin.
• They differentiate into cementoblasts.
• They secrete the organic matrix of collagen
and ground substance which mineralizes.
• The cells of Periodontal ligaments and fibres
also differentiate from dental follicle.

70. FORMATION OF PERMANENT DENTITION
• The permanent teeth also arise from further
proliferation from dental lamina.
• These join the dental organ of deciduous tooth germs.
• This proliferation is usually on the lingual aspect of
deciduous tooth germ.
• The molars of permanent dentition have no deciduous
predecessors. So, the dental lamina burrows
posteriorly and this backward extension gives rise to
tooth germs of first, second and third molars.

71. CLINICAL SIGNIFICANCE
Disturbances due to genetic or environmental
factors during any stage of tooth development
can cause anomalies. such as
Initiation & proliferation (bud and cap stage ):
anodontia , hypodontia, supernumerary teeth,
gemination,

72. Morpho and histo diffrentiation (bell stage ):
disturbance in size and shape of teeth:
• Macrodontia, microdontia, taurodontism ,
Dens-invaginatus,
Maturation and eruption:
• Enamel hypoplasia
• Delayed eruption